Production of improved lubricating oils

ABSTRACT

LUBRICATING OILS OF IMPROVED COLOR, VISCOSITY INDEX AND STABILITY TOWARDS ULTRAVIOLET LIGHT ARE OBTAINED BY A PROCESSING SEQUENCE INVOLVING IN A SPECIFIC EMBODIMENT SOLVENT REFINING A LUBE OIL STOCK, HYDROCRACKING THE SOLVENT REFINED MATERIAL AND SUBJECTING THE HYDROCRACKED PRODUCT TO A SECOND SOLVENT REFINING. SUPERIOR RESULT ARE OBTAINED USING N-METHYL-2-PYRROLIDONE AS THE SOLVENT.

United States Patent 3,652,448 PRODUCTION OF IMPROVED LUBRICATING OILS Billy H. Cummins, Nederland, Tex., assignor to Texaco Inc, New York, N.Y. No Drawing. Filed June 30, 1969, Ser. No. 837,930 Int. Cl. (310g 13/00 US. Cl. 20887 9 Claims ABSTRACT OF THE DISCLOSURE This invention relates to the production of improved lubricating oils. More particularly it is concerned with a process sequence for the production of lubricating oils of high viscosity index having good stability towards ultraviolet light. In one of its more specific aspects, it is concerned with the production of high viscosity index lubrieating oils of good ultraviolet stability from low grade lubricating oil charge stocks using a process sequence which includes solvent refining, hydrocracking, a second solvent refining and then dewaxing.

Various steps for the defining of lubricating oils such as distillation, solvent refining, solvent dewaxing, acid treating and clay contacting are well known. When residual type oils are being processed, a preliminary step of deasphalting is also generally required.

In the processing steps listed above, distillation is employed as a means of separating a crude oil into fractions of various viscosities, solvent refining with, for example, furfural, sulfur dioxide or phenol is ordinarily used as a means of removing aromatic compounds and thereby improving the viscosity index, solvent dewaxing using for example a mixture of methyl ethyl ketone and toluene is used to improve low temperature properties by lowering the pour point of the oil, and clay contacting is used generally as a final step to further improve the color and to neutralize the oil after acid treating.

In a typical operation, a crude oil is topped under atmospheric pressure to produce light distillates and an atmospheric reduced crude which is then vacuum distilled to produce lube oil distillates. The residue from the vacuum distillation is deasphalted to yield residual lubricating stocks. conventionally the various lube oil fractions are then further processed by solvent refining, dewaxing, acid treating and clay contacting.

In conventional lube oil refining the solvent extraction step is carried out first to recover about 4590% of the charge as solvent refined oil and to reject about 10-55% of the charge as dark colored, viscous extract. Since the extract amounts to a relatively high percentage of the charge and is not suitable for up-grading by dewaxing and clay contacting to a satisfactory quality level for use as a lube oil, solvent extraction has, up to the present been the most logical and economical step to apply first. Conventionally the solvent refined oil is contacted with clay to improve its color and then dewaxed although in some instances it may be desirable to dewax prior to clay contacting.

Because of the increasing demand for the lighter grade lubricating oils it has been found advantageous to convert the heavier grade oils to the more valuable lighter products by hydrocracking. However, for not completely known reasons, oils prepared by hydrocracking are not 3,652,448 Patented Mar. 28, 1972 stable to ultraviolet light and form a fiocculent precipitate upon prolonged exposure to sunlight. It is therefore a principal object of this invention to produce by hydrocracking lubricating oils with improved stability to ultraviolet light.

According to my invention a lubricating oil is subjected to solvent refining, the solvent refined oil is hydrocracked and the hydrocracked oil is subjected to a second solvent refining. To lower the pour point of the oil it may then be dewaxed.

The process of the invention is preferably applied to feedstocks consisting of deasphalted vacuum residual and/ or heavy wax distillates.

The feedstock is first subjected to solvent refining with a solvent having an afiinity for aromatic compounds which is at most only partially soluble in the oil so that two phases can be formed, an extract phase containing solvent and dissolved aromatics and a rafiinate phase. Suitable solvents are furfural, nitrobenzene, dimethyl formamide, liquid S0 and the like. For example, furfural is generally used at dosages of 600%, at temperatures between l20-250 F., preferred conditions being dosages of 100- 300% and temperatures between -2l0 F. A particularly suitable solvent is N-methyl-Z-pyrrolidone which can be used at a lower temperature and lower dosage than the other solvents mentioned above. In addition N-methyl- 2-pyrrolidone is preferred because of its chemical stability and its ability to produce even lighter colored refined oils. The other solvents mentioned above have a tendency to produce refined oils that are degraded and darkened in color.

After separation from the extract phase and removal of residual solvent, the rafiinate is then subjected to hydrocracking.

The reaction conditions for the hydrocracking may be varied depending on the amount of hydrocracking desired and on the charge stock. Typical reaction conditions include a temperature of about 700-900 F., preferably 750-850 F. the pressure may range between about 500 and 5000 p.s.i.g., a preferred nange being from 1000 to 2500 p.s.i.g. Space velocities may be between about 0.1 and 10.0 v./v./hr. with a preferred range being 0.31.5. Hydrogen rates of from 1000-10,000 s.c.f..b. have been found satisfactory although rates of 3000l0,000 s.c.f.b. are preferred.

Hydrogen from any suitable source such as electrolytic hydrogen, hydrogen obtained from the partial combustion of hydrocarbonaceous material followed by shift conversion and purification or catalytic reformer by-product hydrogen may be used. The hydrogen should have a purity of between about 50 and 100% with hydrogen purities of 75-9-5 volume percent being preferred.

The oil and hydrogen are brought into contact in the presence of a catalyst. The catalyst may be in the form of a fixed bed, a moving bed, a fluidized bed or may be slurried with the oil. Hydrogen flow may be upward or down- Ward through the reactor as may be the How of the oil. In a specific embodiment both the oil and a portion of the hydrogen are introduced at the top of a reactor containing a fixed bed of the catalyst, the balance of the hydrogen being introduced at intermediate points in the reactor for cooling purposes.

The catalyst for the hydrocracking step preferably comprises a compound of a Group VI metal such as molybdenum, chromium or tungsten or a compound of a Group VIII metal such as cobalt, iron or nickel and mixtures thereof. Ordinarily the catalyst is charged to the reactor in oxide form although it can be expected that some reduction and some sulfidation take place during the course of the process so that after being on stream for some time the catalyst is probably a mixture of the metal, the

metal sulfide and perhaps the oxide. If desired, the catalyst after being charged to the reactor but prior to the institution of the on stream period may be converted at least in part to the sulfide form, for example, by contact with a gas such as a mixture of hydrogen and a sulfiding agent, e.g. hydrogen sulfide, methyl mercaptan or carbon disulfide. The Group VIII metal may be present in an amount varying from 1 to 20% by weight of the total catalyst composite, preferably 2- and the Group VI metal may be present in an amount ranging from about 540%, preferably 7-25 The metal components are supported on a refractory inorganic oxide such as decationized zeolite, alumina, zirconia, silica or magnesia and mixtures thereof optionally promoted with an acidic material such as boron oxide or a halogen.

Advantageously, the catalyst has a surface area of at least 150 m. /g., and a pore volume of at least 0.5 cc./g. The upper limit of the surface area and pore volume is governed by the hardness and ruggedness of the catalyst. As a practical matter, for commercial installations where the catalyst is used in units capable of processing several thousand barrels of charge per day, the surface area probably should not exceed about 800 m. /g. and the pore volume about 0.8 cc./ g.

The catalyst may be prepared by any of the methods well known in the art, such as by impregnating the support with a solution of a salt of one of the metals, filtering, drying and then if desired impregnating with a solution of a salt of another metal, filtering, drying and calcining in a manner well known in the art.

The effluent from the hydrocracker is cooled and hydrogen-rich gas separated therefrom and recycled to the hydrocracking zone. Optionally, the hydrogen-rich stream is scrubbed with water to remove any ammonia contained therein or a portion thereof may be bled from the system to prevent the build-up of ammonia and/or low molecular weight hydrocarbons. Hydrogen is added to the recycle stream to replace that consumed in the hydrocracking reaction and if necessary to replace any hydrogen purged from the system. Lubricating oil fractions are recovered from the balance of the hydrocracker effluent by distillation, if necessary, at reduced pressure.

The solvent refined hydrocracked oil is then subjected to a second solvent refining step. However, in this instance although the various solvents mentioned for the initial solvent refining steps do give improved results, N-methyl-Z-pyrrolidone is outstanding in its ability to impart ultraviolet stability to the oil. The unusual feature of this invention is that solvent refining prior to hydrocracking alone is not sufficient to render the oil stable to ultraviolet light but the second solvent refining, particularly when the solvent is N-methyl-Z-pyrrolidone, results in an improved oil. The solvent refining conditions for the second refining step need not be as severe as those for the first.

After the second solvent refining, the oil may be subjected to dewaxing to reduce its pour point. In one embodiment of our invention, the rafiinate from the second solvent refining is passed into contact with a catalyst comprising a hydrogenating component, such as is used in the hydrocracking catalyst, supported on a decationizied mordenite. Preferably the support is made by treating a synthetic mordenite with acid to replace the sodium ions with hydrogen ions. Advantageously, the synthetic mordenite is treated with acid to the extent that a portion of the alumina is leached out to produce a mordenite having a silicazalumina mol ratio of at least and having increased dewaxing activity. The catalytic dewaxing may be carried out at a temperature of at least 450 F., a pressure of at least 100 p.s.i.g., a space velocity of 0.2-5.0 v./v./hr. and a hydrogen rate of l00010,000 s.c.f.b. Preferred conditions in the catalytic dewaxing zone are a temperature of 450-800 F., a pressure of 100-1500 p.s.i.g. and a space velocity of 0.2-2.0 v./v./hr.

Alternatively, the oil may be contacted with a dewaxing agent such as a mixture containing 40-60 volume percent of a ketone such as acetone, methyl ethyl ketone or normal butyl ketone and 60-40 volume percent of an aromatic compound such as benzene or toluene in a ratio of about 3-4 parts by volume of solvent per volume of oil, the mixture cooled to a temperature of about 0 to 20 F. and the waxy components removed by filtering or centrifuging. The filtrate is then subjected to fiash distillation and stripping to remove the solvent. The resulting product is a lubricating oil of high viscosity index and good stability towards ultraviolet light.

The following examples are submitted for illustrative purposes only.

EXAMPLE I The charge in this example is a furfural refined oil obtained by distillation from a deasphalted vacuum residuum and hydrocracked over a catalyst containing 2.8% nickel and 9.6% molybdenum as the sulfides supported on silica-alumina base (73% silica) having a pore volume of 0.72 cc./g. and a surface area of 349 m. /g., at 750 F., 1800 p.s.i.g., 0.4 v./v./hr. and 6000 s.c.f.b. hydrogen. Table 1 column 1 shows the characteristics of the hydrocracked lube oil, column 2, the dewaxed hydrocracked oil, column 3, the characteristics of an oil obtained by batch refining the hydrocracked oil with N-methyl-Z-pyrrolidone at 180 F. and a dosage of 300% and column 4 the dewaxed raffinate of column 3. This example shows that the fioc formation of the hydrocracked oil in U.V. light is reduced by the mild solvent refining treatment. Additionally the viscosity idex of the oil is improved 12 VI units.

In this example the charge, an oil obtained by propane deasphalting a vacuum residuum is hydrocracked at 785 F., 2300 p.s.i.g., 0.4 v. /v. /hr. and 6000 s.c.f.b. hydrogen over a fixed bed of a catalyst containing 5.9% nickel and 18.3% tungsten on an alumina support having a surface area of 171 mfi/g. and the hydrocracked product is then dewaxed using a 50:50 mixture of methyl ethyl ketone and benzene at a 3:1 dilution and a temperature of 30 F.

In Table 2, below, column 1 lists the characteristics of the dewaxed hydrocracked oil, column 2, those of the rafiinate obtained by batch furfural refining the dewaxed hydrocracked oil at a dosage of 300% at F. and column 3 those of the raffinate obtained by batch solvent refining the dewaxed hydrocracked oil at a dosage of 300% of 150 F. with N-methyl-Z-pyrrolidone.

TABLE 2 5 0. No 1100 but hazy" No 1100, clear.

U.V. stability, 48 hrs TABLE 3 Viscosity:

BUS/100 F.--'.-'.;' 466 469. SUB/210 F-- 61.9 64.5. Viscosity index 98 110. Pour, F 20 +5.

U.V. stability, 48 hours F100 No floc.

EXAMPLE IV This example shows that solvent refining lube hydrocracked oil with N-methyl-Z-pyrrolidone results in much improved color. The oil in this example is obtained by butane decarbonizing a vacuum resid from a sweet Louisiana crude, hydrocracking the decarbonized residuum, and solvent refining with N-methyl-Z-pyrrolidone. The solvent refining is conducted on a 12 stage mixersettler countercurrent extractor using 105 volume percent solvent and 120 F., extraction temperature. The refined oil is produced in 82 volume percent yield. Properties of the hydrocracked oil before and after solvent refining are shown in columns 1 and 2, respectively.

TABLE 4 Gravity, API 31. 1 35. 2 Viscosity:

SUB/100 F.* 62. 7 67.6 sUs/210 F 35. 5 36. 7 Viscosity index. 106 130 Color, Lovi 130/112 5/6 'Extrapolated.

I claim:

1. A process for the production of a lubricating oil of high viscosity index and good ultraviolet light stability which comprises solvent extracting a deasphalted residuum with a solvent having an affinity for aromatic compounds to produce an extract containing dissolved aromatics and a ralfinate, hydrocracking the rafiinate at a temperature between about 750 and 850 F. and then subjecting the hydrocracked rafiinate to a solvent extraction using N-methyl-Z-pyrrolidone as the solvent.

2. The process of claim 1 in which the second solvent refining is carried out at milder conditions than the first.

3. The process of claim 1 in which the solvent in the first solvent refining step is furfural.

4. The process of claim 1 in which the solvent in the first solvent refining step is N-methyl-Z-pyrrolidone.

5. The process of claim 1 in which after the second solvent refining, the oil is subjected to a dewaxing treatment.

6. The process of claim 1 in which the hydrocracking is carried out in the presence of a catalyst comprising a Group VIII metal or compound thereof.

7. The process of claim 6 in which the hydrocracking catalyst comprises nickel and molybdenum.

8. The process of claim 6 in which the catalyst comprises nickel and tungsten.

9. The process of claim 6 in which the catalyst comprises nickel and molybdenum.

References Cited UNITED STATES PATENTS 3,242,068 3/1966 Paterson 20818 3,414,506 12/1968 Campagne 20818 3,463,724 8/ 1969 Langlois et al 208'18 3,472,757 10/1969 Morris et a1 208-18 HERBERT LEVINE, Primary Examiner US. Cl. X.R. 

